The invention relates generally to the field of connection-orientated data networks and more particularly to a method and apparatus for converting a permanent connection, such as a permanent virtual circuit, into a signalled permanent connection, such as a soft permanent virtual circuit, particularly within an asynchronous transfer mode (ATM) network.
A permanent connection, such as a permanent virtual circuit or PVC, comprises a series of interconnected bearer channels (hereinafter xe2x80x9cbearer channel pathxe2x80x9d) which exists for a long time between two or more end-stations and is set up through subscription with a service provider. The service provider defines or provisions the permanent connection manually, or alternatively through the use of a network management system (NMS) which is linked to all of the network elements or nodes. If the permanent connection is manually commissioned, the system operator must manually select the route for the bearer channel path across the network. Then, through the use of a network management terminal interface (NMTI), the system operator must manually configure and establish each individual bearer channel cross-connection on each node by setting or adjusting its routing table and allocating the appropriate amount of connection bandwidth. Next, the bearer channel identifiers, e.g. VPI/VCI, used by the end-stations for information transfer must be manually allocated and reported thereto. In addition, in the event of a failed link between nodes, the many bearer channel paths carried by the link must generally be manually re-routed, which can be quite a difficult chore.
The NMS offers many advantages over the manual commissioning of cross-connects. In particular, the NMS is capable of automatically computing the route across the network for the bearer channel path and automatically configuring and establishing the individual cross-connects. In addition, because the NMS is connected to each node through an overlay network, the nodes can inform the NMS about a failed link and it can automatically reroute bearer channel paths associated with the failed link. Due to the efficacy of the NMS, most sizeable permanent connection networks employ such as device. A commercially available example of a network management system is the MainStreet Xpress(trademark) 46020 Network Manager manufactured by Newbridge Networks Corporation of Kanata, Ontario, Canada.
A switched connection, such as a switched virtual connection or SVC, is created and released on-the-fly by the end-stations and nodes through the exchange of a series of signalling messages using a signalling protocol. The signalling between nodes is carried over a signalling network comprising call control infrastructure disposed on each node, and signalling links, such as a dedicated PVC, for interfacing or communicating between similar infrastructure disposed on counterpart nodes. Generally, the signalling messages include a xe2x80x9ccall set-upxe2x80x9d message sent by the originating end-station to the destination end-station across the network. The call set-up message includes, among other things, the destination address and quality of service parameters. In hop-by-hop routing, each node which receives the call set-up message consults a routing table resident thereon in order to determine the next hop and bearer channel link towards the destination end-station, and establishes the bearer channel cross-connect. In source routing, the ingress node maintains a database representative of the topology of the network and specifies the path, and optionally the links, for the call in the call set-up message. Thus, each node which receives the call set-up message is directed to progress it to the next node in the pre-specified path. Irrespective of which method of routing is used, the call will steer itself through the network to the destination end-station which will send an acknowledgement, such as a reply xe2x80x9cconnectxe2x80x9d message, back to the originating end-station. A further xe2x80x9cconnect acknowledgexe2x80x9d message may be sent to the destination end station from the originating end station. As a result of this exchange of messages, bandwidth is allocated and an end-to-end uni- or bi-directional bearer channel path is thereby established. At the end of the information transfer, the bearer channel for the call may be tom down, i.e, the cross-connects are dismantled, by another series of signalling messages.
Recently, standards have been adopted to provide signalled permanent connection capability such as signalled permanent virtual circuits or S-PVCs (alternatively referred to as xe2x80x9cSPVCxe2x80x9d or xe2x80x9csoft permanent virtual circuitsxe2x80x9d). An S-PVC is provisioned by the system operator, either directly through the NMTI or indirectly through the NMS, but the bearer channel path and the cross-connects thereof are established by signalling in a manner similar to that of an SVC. More particularly, the S-PVC is typically commissioned by instructing an ingress node (via the NMTI or NMS ) to initiate the S-PVC. The call control infrastructure on the node creates an S-PVC call set-up message (e.g. for hop-by-hop or source routing), which is similar to the SVC call set-up message, and sends it over the signalling network to the next node, which does the same. In this manner the bearer channel path is signalled across the network until it reaches the egress node. The egress node is able to resolve the destination address specified in the S-PVC call set-up message, and sends an acknowledgement back to the source node, and thereby, to the system operator. The edge nodes do not, however, signal the end-stations over the user-to-network interfaces (UNIs) therebetween (assuming the end-stations support UNI signalling) as in the case of an SVC. Thereafter, the end-stations can be manually configured to transmit the provisioned bearer channel identifiers.
The S-PVC is attractive to the service provider because, from the view point of the customer, who is not concerned how the bearer channel is created, it appears that a PVC has been provided. However, the S-PVC provides a robust and efficient path management strategy. In particular, in the event of a failed link between nodes, an S-PVC can be automatically re-routed by the network through the use of the signalling protocol. For example, when the ingress node receives a message to release the S-PVC and the indicated cause for the release is a link failure, the ingress node can consult its resident routing table, select an alternate path, and re-signial the S-PVC call set-up message. Reroutes can be accomplished significantly faster using the distributed computing power of the network than by the NMS. In addition, the recent move by the industry to the adoption of standards such as the ATM Forum P-NNI protocol to enable nodes to dynamically exchange routing information, and hence keep up to date about network conditions, allows for a more robust network recovery mechanism.
Accordingly, with the advent of signalled permanent connections capability such as S-PVCs, the need for a network management system providing centralized bandwidth management for the establishment of bearer channel paths is lessened. In short, S-PVCs are taking over where centralized PVC strategies were once used. However, there are many large legacy PVC networks in existence comprising many thousands of permanent connections. In the prior art, if the service provider wished to convert on existing PVC network into an S-PVC network, each PVC had to be manually disconnected and re-established as an S-PVC path. This is very time consuming in terms of manual operator time and the amount of time the bearer channel paths are unavailable to customers. Also, since the S-PVC path is defined and managed by the network, there is no guarantee that the original cross-connects and bearer channel identifiers, e.g. VPI/VCIs, will be used by the new S-PVC paths, thus requiring much work to manually re-configure the end-stations.
Broadly speaking, the invention provides a method of converting a permanent connection, such as a PVC, into a signalled permanent connection, such as an S-PVC, in a connection-orientated network, such as an ATM network. The method comprises the steps of: (a) establishing signalling links between each network node along a permanent connection path; (b) providing information to identify the cross-connections along the path; (c) incorporating the cross-connect identification information in a call set-up message; (d) transmitting the call set-up message along the path from a source network node to a destination network node; and (e) associating the cross-connection of each node along the path with the appropriate signalling links in order to form the signalled permanent connection. The cross-connect identification information may be a unique call identifier for the permanent connection, in circumstances where the call identifier is associated with each permanent connection cross-connection prior to step (d). Alternatively, the cross-connect identification information may be a permanent connection path definition specifying each cross-connection in the path.
Another aspect of the invention relates to an apparatus for converting a permanent connection into a signalled permanent connection in a connection-orientated network comprising interconnected network nodes. The apparatus comprises signalling means for communicating signalling messages between network nodes along a permanent connection path. A network management system is connected to the network nodes along the path, and includes means for providing information to identify a bearer channel cross-connection made on each network node along the path. Call processing means are distributed on each node along the path for incorporating the cross-connect identification information in a call set-up message, signalling the call set-up message along the path from a source node to a destination node, and associating the cross-connection identified on each node along the path with the signalling means to form the signalled permanent connection.
In the preferred embodiment, the network management system (NMS) maintains a database of all PVCs and their paths in an ATM network. The NMS establishes a unique identifier for each PVC in the network and transmits the unique identifier to each node along the path of a given PVC. The nodes tag or otherwise associate the unique identifier of each PVC with the corresponding bearer channel cross-connects established thereon. Means are provided for establishing ATM signalling links between each pair of nodes in the network. The NMS instructs the ingress node of each PVC to signal over the signalling links a source-routed, S-PVC call set-up message, which includes the unique PVC identifier and a xe2x80x9cconvert PVC into S-PVCxe2x80x9d instruction. Each node, including the ingress node, which receives this S-PVC call set-up message searches for an active cross-connect that has been previously labelled or tagged with the unique call identifer and, if a match is found, uses the existing, tagged, cross-connect to progress the S-PVC call set-up. When the S-PVC call set-up message reaches the destination or egress network node, an acknowledging connect message is sent back to the ingress node and it signals the successful conversion of the corresponding PVC into an S-PVC to the NMS. Thereafter, the NMS deletes the converted PVC from the NMS database.